1. Field of the Invention
The invention relates to a method of thin film processing and, more particularly, to a method of forming an integrated titanium/titanium nitride film structure.
2. Description of the Background Art
In the manufacture of integrated circuits, a titanium nitride film is often used as a metal barrier layer to inhibit the diffusion of metals into an underlying material beneath the barrier layer. These underlying materials form transistor gates, capacitor dielectrics, semiconductor substrates, metal lines, and many other structures that appear in integrated circuits.
For example, when an electrode is being formed for a transistor's gate, a diffusion barrier is often formed between the gate electrode and a metal that serves as the contact portion of the electrode. The diffusion barrier inhibits the diffusion of the metal into the gate electrode material, which may be composed of polysilicon. Such metal diffusion is undesirable because it would change the characteristics of the transistor, or render it inoperative. A combination of titanium/titanium nitride (Ti/TiN), for example, is often used as a diffusion barrier.
The Ti/TiN stack has also been used to provide contacts to the source and drain of a transistor. For example, in a tungsten (W) plug process, a Ti layer is deposited upon a silicon (Si) substrate, followed by conversion of the Ti layer into titanium silicide (TiSi.sub.x), which provides a lower resistance contact with Si. A TiN layer is then formed upon the TiSi.sub.x layer, prior to forming the tungsten plug. In addition to being a barrier layer, the TiN layer serves two additional functions: 1) prevents chemical attack of TiSi.sub.x by tungsten hexafluoride (WF.sub.6) during W deposition; and 2) acts as a glue layer to promote adhesion of the W plug.
Ti and TiN films can be formed by physical or chemical vapor deposition. A Ti/TiN combination layer may be formed in a multiple chamber "cluster tool" by depositing a Ti film in one chamber followed by TiN film deposition in another chamber without exposing the Ti film to the atmosphere, i.e., an integrated Ti/TiN deposition process. When depositing both Ti and TiN using chemical vapor deposition (CVD), titanium tetrachloride (TiCl.sub.4), for example, may be used to form both Ti and TiN films when allowed to react with different reactant gases, e.g., hydrogen (H.sub.2) for Ti deposition under plasma condition, and ammonia (NH.sub.3) for TiN thermal deposition.
However, when a TiCl.sub.4 -based chemistry is used in such an integrated Ti/TiN film deposition process, a reliability problem is encountered. In particular, the integrated Ti/TiN stack structure tends to either peel off or exhibit a haze, which may result, for example, from TiCl.sub.4 or other species arising from TiCl.sub.4, chemically attacking the Ti film prior to TiN deposition.
Therefore, there is a need in the art for methods of Ti/TiN process integration having improved film characteristics.